Method for making polished gemstones and an abrasive material for doing same

ABSTRACT

A method for shaping a gemstone comprising the steps of 1) attaching a gemstone to a dop, 2) holding the gemstone against a rotating lap wheel, and 3) shaping the gemstone on the lap wheel. The surface of the lap wheel is a metal abrasive material comprising a base having a plurality of pyramidal shapes protruding therefrom, a portion of the protrusions having a substantially polygonal base and triangular sides which meet at an apex which substantially forms a point, hereinafter pyramidal protrusions, and a portion of the protrusions having a substantially polygonal base and substantially trapezoidal sides with the portion thereof distant from the base surface forming a plateau such that the protrusions are substantially butte-like in shape, hereinafter termed butte protrusions, the protrusions providing intermixing cutting and planing edges, the ratio of the pyramidal protrusions to the butte protrusions ranging from 100:0 to 0:100. Also provided is the metal abrasive material used to carry out the method.

FIELD OF THE INVENTION

The present invention relates to a method of faceting, shaping andpolishing gemstones. The present invention also relates to abrasivematerials for faceting and polishing precious gemstones and for shapingand polishing semi-precious gemstones.

BACKGROUND OF THE INVENTION

Precious gemstones include diamonds, rubies, emeralds and sapphires.

Diamonds have the greatest hardness of any gemstone with a hardness of10 on the Moh's scale. Rough diamonds are generally cleaved, i.e., splitalong the grain, using a thin steel knife blade or sawn using a diamondsaw or laser to separate the rough diamond into individual pieces.

This is followed by rough shaping by bruting, i.e., grinding a cleaveddiamond against a cleaved diamond to form each into a round shape orrubbing a cleaved diamond with another diamond or diamond chip to form afancy shape such as a square or rectangle. Then, facets are polishedonto the diamond using a revolving horizontal metal wheel, or lap,charged with diamond dust and oil.

Lap wheels, or laps are also used for faceting other precious gemstones,including rubies, emeralds, and sapphires, as well as more transparentsemi-precious gemstones, such as, for example, amethyst, topaz, garnet,aquamarine, tourmaline, and citrine.

Gemstones which are opaque and generally softer than gemstones which arefaceted are shaped as cabochons, usually flat on the back side and domedon the face with an elliptical or a round shape. Modifications or theelliptical or round shapes are occasionally used to avoid flaws in thestones, emphasize particular color variations in the stone, or toprovide shapes such as hearts or teardrops. Cabochons are cut to shapeusing a band saw or trim saw. The back side is polished flat and theface is then shaped and polished using a lap wheel. The abrasivematerial used on the lap surface is usually particulate, either bondedto a backing or charged onto the lap wheel surface.

For faceting, the gemstone is customarily held on a dop, an elongatedshaft, using an appropriate glue, and fastened into a holder on a flatlap machine at a specific angle against the abrasive lap surface toproduce the facet. The dop is rotated and moved as necessary to producethe desired faceting on the gemstone. In shaping cabochons, the gemstoneis also held on a dop with glue or wax, but is normally hand held androtated against the abrasive lap surface. Typically, the lap wheel iscooled and/or lubricated with oil or water depending on the gemstonebeing faceted or formed into a cabochon. Both faceting gemstones andforming gemstone cabochons will hereinafter be termed “shaping”gemstones, unless necessary to be specific for clarity.

SUMMARY OF THE INVENTION

The present invention, in one aspect, provides a method for shaping agemstone comprising the steps of

-   -   1) attaching a gemstone to a dop,    -   2) holding the gemstone against a rotating lap wheel, and    -   3) shaping the gemstone on the lap wheel,        wherein the surface of the lap wheel is a metal abrasive        material comprising a base having a plurality of pyramidal        shapes protruding therefrom, a portion of the protrusions having        a substantially polygonal base and triangular sides which meet        at an apex which substantially forms a point, hereinafter        pyramidal protrusions, and a portion of the protrusions having a        substantially polygonal base and substantially trapezoidal sides        with the portion thereof distant from the base surface forming a        plateau such that the protrusions are substantially butte-like        in shape, hereinafter termed butte protrusions, the protrusions        providing intermixing cutting and planing edges, the ratio of        the pyramidal protrusions to the butte protrusions ranging from        100:0 to 0:100.

The metal abrasive, having a base unitary with the protrusions, ispreferably formed from metal alloys such as, for example, stainlesssteel, spring steel, cold rolled steel, titanium alloys, and molybdenumalloys. Particularly preferred are stainless steel and spring steel.

The abrasive protrusions, unitary with the base, may be arranged inrows, spiral, helix, or lattice fashion, or may be randomly spaced. Thearrangement, height, and shape or the abrasive protrusions helps todefine the rate of surface removal in shaping the gemstone.

The protrusions of the abrasive material useful in the invention may bethe same or different in shape. For example, various protrusions mayhave different bases configurations, i.e., different numbers of sides,and/or different degrees of slope with some bases approaching a circularshape. Generally, a triangular base is preferred. The triangular sidesof the pyramidal protrusions and the trapezoidal sides of the butteprotrusions may have an inward arcuate slope.

The abrasive material useful in the invention may be subjected to highand/or low temperature treatment. Heat treatment, i.e., annealing isparticularly useful to remove stress in cold rolled steel. Optionalperformance enhancing surface treatments may be applied to theprotrusions and the base surface to improve abrasive performance,increase abrasive endurance, aid in non-loading characteristics due tothe lubricity of certain coatings, and reduce surface porosity.

The abrasive material for use on a lap machine is provided as a diskusually 6 inches or 8 inches in diameter although disks as large as 12inches in diameter or larger may be used. The abrasive material can beadhered to the lap wheel by means well known to those skilled in theart. The abrasive material may also be in the form of a small diskpreferably having a diameter of from about 0.5 inch to about 1.5 inches,more preferably from about 0.75 inch to 1 inch or in the form of a smalldrum preferably having a diameter of from about 0.5 inch to about 1.5inches, more preferably from about 0.75 inch to 1 inch for use with ahand held high-speed rotary tool. A hand held high-speed rotary tool issuitable for use in the method of the invention for producing cabochonswith shapes such as, for example, hearts or crosses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are perspective views of pyramidal protrusionssuitable for the abrasive material useful in the method of the presentinvention.

FIG. 2A is a cross-sectional view of an abrasive material havingpyramidal protrusions on both surfaces thereof useful in the presentinvention.

FIG. 2B is a cross-sectional view of an abrasive material inventionhaving pyramidal protrusions of varying heights on the surface thereofuseful in the present.

FIG. 3 is cross-sectional view of a pyramidal protrusion having aperformance enhancing coating thereon useful in the present invention.

FIG. 4A is a perspective view of a pyramidal protrusion havingtriangular sides with a slope of about 30° which meet at an apex whichsubstantially forms a point useful in the present invention.

FIG. 4B is a perspective view of a pyramidal protrusion havingtriangular sides with a slope of about 20° which meet at an apex whichsubstantially forms a point useful in the present invention.

FIG. 4C is a perspective view of a preferred pyramidal protrusion usefulin the present invention having triangular sides with a slope of about40° which meet at an apex which substantially forms a point.

FIG. 5A is a cross-sectional view of a butte protrusion having a slopeof about 45° and a plateau distant from the base surface an amountequivalent to 90% of a pyramidal protrusion having a 45° slope.

FIG. 5B is a cross-sectional view of a butte protrusion having a slopeof about 45° and a plateau distant from the base surface an amountequivalent to 80% of a pyramidal protrusion having a 45° slope.

FIG. 5C is a cross-sectional view of a butte protrusion having inwardarcuate sides and a plateau distant from the base surface an amountequivalent to 70% of a pyramidal protrusion with a 45° slope.

FIG. 6A is a fragmented top view of a portion of a mask suitable for usein producing an abrasive material suitable for use in the presentinvention.

FIG. 6B is a fragmented top view of the mask shown in FIG. 6A enlarged400×.

FIG. 6C is a fragmented top view of an abrasive material enlarged 400×having pyramidal protrusions which can be produced using the mask shownin FIGS. 6A and 6B.

FIG. 6D is a fragmented top view of an abrasive material enlarged 400×having butte protrusions with plateaus distant from the base surface anamount equivalent to 80% of the height of a pyramidal protrusion havinga similar slope which butte protrusions can be produced using the maskshown in FIGS. A and 6B.

FIG. 7A is a fragmented top view of a portion of an abrasive materialuseful in the present invention.

FIG. 7B is a fragmented top view of a mask enlarged about 400× usefulfor producing the abrasive shown in FIG. 7A.

FIG. 8 is a fragmented top view of an abrasive disk useful in thepresent invention with a portion shown at 400×.

FIG. 9 is a fragmented top view of an abrasive disk useful in thepresent invention with a portion shown at 400×.

FIG. 10A is a top view of a disk useful in the present invention.

FIG. 10B shows the disk of FIG. 10A enlarged about 400×.

FIG. 11A is a top view of a disk useful in the present invention.

FIG. 11B shows the disk of FIG. 11A enlarged about 400×.

FIG. 12A is a side view of an abrasive material for use as a drumabrasive in the present invention.

FIG. 12B is a perspective view showing the manner in which the abrasivematerial of FIG. 12A is used to form a cylindrical drum.

DETAILED DESCRIPTION OF THE INVENTION

In the method for shaping gemstones of the present invention, theabrasive material is formed from metal alloys such as, for example,stainless steel, spring steel, cold rolled steel, titanium alloys, andmolybdenum alloys. Particularly preferred are stainless steel and springsteel.

Stainless steel and spring steel are a particularly preferred basematerials in the present invention due to the intrinsic resistance ofthe material to corrosion and the ability of the metal to be readilyreproducibly etched to form the abrasive material useful in theinvention.

The method of the present invention is distinctly advantageous in thatthe abrasive used is formed by etching a pattern of protrusions from thematerial which forms the base, i.e. the abrasive substrate. Whenfaceting the harder gemstones using prior methods, abrasive particulateis charged on a wheel with oil and, as the faceting process progresses,additional abrasive particulate and oil are added to maintain theabrasiveness of the wheel. When shaping softer gemstones using priorabrasive materials, e.g., sandpaper and sanding disks which haveparticulate such as, for example, garnet, aluminum oxide, silicon oxide,and other hard abrasive particles, adhered to a backing by a bindersystem, the particulate is dislodged from the surface of the abrasive.Such loss of abrasive particulate results in deterioration of theabrasive material.

The etching process can be carried out using resist and etchingmaterials and processes which are well known to those skilled in theart. Prior to application of the photoresist to the base material,cleaning of the base material is preferably carried out. The resistcoating can be applied using, for example, hot roll lamination, screenprinting, gravure printing, dip coating and the like.

The mask which is used to provide the desired abrasive pattern surfaceis then placed on the resist covered base material. Good, i.e.,intimate, contact between the resist coating and the mask is needed toachieve the desired pattern on the base material where the photoresistnot covered by the mask is cured. Curing, or imaging, is achieved byexposure to light sufficient to cure, i.e., cross-link, the polymericresist. The mask is then removed from the base material/photoresist/maskcomposite and the uncured photoresist is removed from the base materialusing a developing solution, or developer. If desired, the photoresistthen remaining on the base material may be imaged again prior to etchingto further ensure good adhesion of the photoresist to the base materialduring etching.

Etching is then performed on those portions of the base material notprotected by the photoresist. The degree of etching can be adjusted byaltering the concentration and temperature of the etchant solution andthe method of application as is known to those skilled in the art. Asetchant removes the base material, a certain portion of the basematerial under the mask also is exposed.

The rate of etching and the extent to which this is allowed to continuedetermines the shape of the protrusions. To achieve the pyramidalprotrusions requires etching to a greater extent than etching to achievethe butte protrusions. To achieve mixed pyramidal protrusions and butteprotrusions, having mask portions of differing surface areas can be usedwith larger mask areas producing butte protrusions and smaller maskareas producing pyramidal protrusion.

The rate of etching also determines the extent to which an inwardarctuate slope is formed. Generally, a faster rate of etching results ina greater inward arc.

On thinner base materials where only one side of a substrate carries theabrasive pattern, both side of the base material may be etched toequalize metal stresses and reduce curling.

After etching, any remaining photoresist may be removed by techniqueswell known to those skilled in the art.

The thickness of the abrasive material is not particularly limited, butafter etching should be suitably stiff when used as a flat abrasive. Ofcourse, stiffness can be provided, if necessary, by attachment to astiff substrate such as, for example, a metal plate or synthetic resinplate having suitable stiffness.

In the method of the present invention the surface of the abrasivematerial can be heat treated, cryogenically treated or heat treated andcryogenically treated or metallurically altered, e.g., case hardening,for example, to form a thin harder layer on the surface of the basesurface and protrusions to improve hardness as is well known to thoseskilled in the art.

Performance enhancing coatings may optionally be applied to the surfaceof the abrasive useful in the present invention. Preferred coatingsinclude, for example, titanium nitride, chromium nitride, boron nitrideand diamond or diamond-like coatings. Such coatings may be applied, forexample, by chemical vapor deposition, plasma-assisted chemical vapordeposition, hypersonic plasma particle deposition, or physical vapordeposition, as appropriate for material being deposited as is well knownin the art. Performance enhancing coatings such as, for example, nickelor chrome plating or plating in combination with diamond dust may alsobe applied to the abrasive material for use in the invention.Performance enhancing coatings are particularly preferred when theabrasive material is used for faceting precious gemstones and othergemstones having higher Moh's hardness.

With respect to the drawings, like references number will be used withreference to like parts.

FIGS. 1A, 1B, and 1C depict various possible embodiments of thepyramidal protrusions of the abrading material of the invention with thebases of the pyramidal protrusions being triangular, square andpentagonal, respectively. Of course, other polygonal shapes can be used.In FIG. 1A, protrusion 10 a is shown having triangular base 12 a,triangular side 14 a, and apex 16 a. In FIG. 1B, protrusion 10 b isshown having square base 12 b, triangular side 14 b and apex 16 b. InFIG. 1C, protrusion 10 c is shown having polygonal base 12 c, triangularside 14 c and apex 16 c. The protrusion can also have a base approachinga circle.

FIG. 2A depicts abrasive material 20 a useful in the invention havingpyramidal protrusions on both sides of base 22 a with sides 24 a andapexes 26 a extending from base 22 a. In FIG. 2B, abrasive material 20 bwith pyramidal protrusion 22 b having side 26 b and having a certainelevation from base 24 b and pyramidal protrusion 23 b having side 27 band having a lesser elevation from base 24 b. Of course, butteprotrusions or mixed pyramidal protrusions and butte protrusions may beformed of varying heights on a substrate surface.

FIG. 3 shows abrasive material 30 having pyramidal protrusion 32 withheight H and base width W on base 34 having a thickness B. On thesurface of protusion 32 and exposed base 34 is performance enhancingcoating 38.

Preferably, the slope of the sides of the pyramidal protrusions or thebutte protrusions can vary from slight, e.g., about 20° or less to about45° , more preferably from about 25° to about 40° , most preferably fromabout 30° to 35° . In FIGS. 4A, 4B, and 4C, the slopes of the sides ofthe pyramidal protrusions are 30°, 20° and 40°, respectively. The slopeof the sides of the protrusions can be controlled by the adhesion of thecured photoresist and the rapidity of the formation of the protrusions.For example, when etching a stainless steel sheet with a ferric chloridesolution, a protrusion having a lesser slope can be formed by using aphotoresist which may have lower adhesion and/or adjusting the ferricchloride to etch more slowly.

FIGS. 5A, 5B, and 5C depict various types of butte protrusions of theabrasive material useful in the method of the present invention havingvarying amounts of height compared to comparable pyramidal protrusions.In FIG. 5A, protrusion 50 a is shown having side 52 a, base 54 a, a flattop portion 56 a and height about 90% of that of a pyramid withcomparable slope. In FIG. 5B, protrusion 50 b is shown having side 52 b,base 54 b, a flat top portion 56 b and height about 80% of that of apyramid with comparable slope. In FIG. 5C, protrusion 50 c is shownhaving side 52 c, base 54 c, a flat top portion 56 c and height about70% of that of a pyramid with slope extending from the base to the outeredge of flat top portion 56 c. However, in FIG. 5C, etchant has removedsubstrate material from under the photoresist which covered portion 56C,to leave undercut 58 c. On a pyramidal protrusion where etchant removessome material under the photoresist, an inward arctuate slope of theside would result.

FIG. 6A shows a portion of an abrasive material for use in the presentinvention. In FIG. 6B, enlarged mask portion 60 b, which mask patterncan be used to produce the abrasive material of FIG. 6A, has clearportions 61 b′ which allow the light to pass through to cure thephotoresist. Surrounding the clear portions are the opaque portions 63b′ which prevent curing of the photoresist.

After curing of the photoresist and removal of the mask, the uncuredphotoresist is removed by rinsing with a solution appropriate for thephotoresist used. The substrate etches, when subjected to an etchantbath, such that pyramidal protrusions or butte protrusions are formedunder the areas of the cured photoresist with the base surface beingformed in the areas having no photoresist. In some cases where pyramidalprotrusions are being formed, the photoresist may be removed during theetching process.

In FIG. 6C, an abrasive material useful in the present invention isshown enlarged 400×. Abrasive material 60 c, which can be produced usinga mask as shown in FIG. 6B, has pyramidal protrusions 61 c extendingfrom base 63 c. In FIG. 6D, another abrasive material useful in thepresent invention is shown enlarged 400×. Abrasive material 60 d, whichcan be produced using a mask as shown in FIG. 6B, has butte protrusions65 d extending from base 63 d. Protrusions 65 d are similar in shape toprotrusion 50 b shown in FIG. 5B.

In FIG. 7A, a portion of an abrasive material useful in the presentinvention is shown. A mask portion shown enlarged 400× in FIG. 7B issuitable for use in making the abrasive material shown in FIG. 7A. InFIG. 7B, enlarged mask 70 b has clear portions 71 b′ which allow thelight to pass through to cure the photoresist. Surrounding the clearportions are the opaque portions 73 b′ which prevent curing of thephotoresist. After etching, protrusions are formed in the areas of curedphotoresist, with base material remaining in the etched areas having noprotoresist.

FIG. 8 is a top view of a portion of an abrasive disk 80 useful in thepresent invention. Disk 80 has a diameter of about 6 inches and may beattached to a lap machine at arbor 85. A portion of the disk enlargedabout 400× shows the footprint of protrusions 81 on base 83.

FIG. 9 is a top view of a portion of an abrasive disk useful in thepresent invention having a pattern different from that shown in FIG. 8.The disk has a diameter of about 10 inches and the detail can be seenmore clearly in the portion shown at 400×.

FIGS. 10A and 11A show small disks for use on a hand held high-speedrotary tool. FIGS. 10B and 11B show disks 10A and 11A, respectively, atabout 400× such that the abrasive pattern is more visible.

FIG. 12A shows an abrasive material for use on a drum attachment of ahand held high-speed rotary tool. FIG. 12B depicts the manner in whichthe abrasive material shown in FIG. 12A is welded at weld line 129 b tosuitably be used on the drum attachment.

EXAMPLES Example 1

A sheet of 420 spring tempered stainless steel having a thickness ofabout 0.032 inch was cleaned and passivated. A photoresist solution wascoated onto the passivated stainless steel and dried. A mask havingpattern as shown in FIG. 6B was applied over the photoresist.

The stainless steel/photoresist/mask composite was exposed to 60millijoules of light to effect imaging of the photoresist. Theunexposed, uncrosslinked photoresist was then removed by rinsing with adeveloper solution. The stainless steel having the photoresist patternthereon was re-exposed to 100 millijoules light to ensure adherence ofthe photo resist to the stainless steel during etching.

The stainless steel was etched to a depth of about 0.012 inch using 36Baume ferric chloride solution at a temperature of 145° F. The resultingetched sheet was rinsed with water and the remaining photoresist wasremoved using an aqueous potassium hydroxide stripping solution.

The etched stainless steel was coated with titanium chromium nitride ata temperature of about 500° F. and subsequently cryogenically cooled at−300° F.

The resulting abrasive material had pyramidal protrusions withtriangular bases. The height of the apexes of the protrusions from thebase material was about 0.002 inch and a slope of about 30°. Theresulting abrasive material was a coarse gemstone abrasive. The materialwas satisfactory for cutting into disks for use on a lap wheel.

Example 2

A sheet of 420 spring tempered stainless steel having a thickness ofabout 0.020 inch was cleaned and passivated. A photoresist solution wascoated onto the passivated stainless steel and dried. A mask havingpattern like that of FIG. 7B was applied over the photoresist.

The stainless steel/photoresist/mask composite was exposed to 60millijoules of light to effect imaging of the photoresist. Theunexposed, uncrosslinked photoresist was then removed by rinsing with adeveloper solution. The stainless steel having the photoresist patternthereon was re-exposed to 100 millijoules light to ensure adherence ofthe photo resist to the stainless steel during etching.

The stainless steel was etched to a depth of about 0.003 inch using 36

Baume ferric chloride solution at a temperature of 145° F. The resultingetched sheet was rinsed with water and the remaining photoresist wasremoved using an aqueous potassium hydroxide stripping solution.

The etched stainless steel was coated with titanium chromium nitride ata temperature of about 500° F. and subsequently cryogenically cooled at−300° F.

The resulting abrasive material had pyramidal protrusions withtriangular bases. The height of the apexes of the protrusions from thebase material was about 0.002 inch and the slope of the sides of theprotrusions was about 30°. The resulting abrasive material was a finegemstone abrasive. The material was satisfactory for cutting into disksfor use on a lap wheel.

Although the present invention has been described with reference topreferred embodiments, it will be understood that various modificationsmay be made without departing from the spirit and scope of theinvention.

1. a method for shaping a gemstone comprising the steps of 1) attachinga gemstone to a dop, 2) holding the gemstone against a rotating lapwheel, and 3) shaping the gemstone on the lap wheel, wherein the surfaceof the lap wheel is a metal abrasive material comprising a base having aplurality of pyramidal shapes protruding therefrom, a portion of theprotrusions having a substantially polygonal base and triangular sideswhich meet at an apex which substantially forms a point, hereinafterpyramidal protrusions, and a portion of the protrusions having asubstantially polygonal base and substantially trapezoidal sides withthe portion thereof distant from the base surface forming a plateau suchthat the protrusions are substantially butte-like in shape, hereinaftertermed butte protrusions, the protrusions providing intermixing cuttingand planing edges, the ratio of the pyramidal protrusions to the butteprotrusions ranging from 100:0 to 0:100.